Circular tracking method for robot

Abstract

A method of tracking a robot with respect to a circularly moving workpiece W. When a workpiece on a disc-shape conveyer remains stationary at a reference position W0, positions P0 and Q0 are taught to the robot in a stationary coordinate system Σ0 and the robot is placed on stand-by at a position A. The angular displacement of the disc-shape conveyer is detected by a pulse encoder and counting of the output pulses starts when the workpiece W arrives at the reference position W0. A CPU of a robot controller reads the counted amount in a short cycle and transforms it into a rotation amount θ of the conveyer from the reference position. Updating of matrix data for setting a rotary coordinate system Σrot based on the rotation amount θ is repeated. When the workpiece W reaches the reference position W0, the CPU executes interpolation calculation for successively determining a target point to which the robot is moved, based on the position data of the waiting position and the position data of teaching points P0 and Q0. The position data obtained by the interpolation calculation in the rotary coordinate system Σrot is converted into the position data in the stationary coordinate system Σ0 and the position of the robot is controlled based on thus obtained position data.

What is claimed is: 
     
       1. A robot tracking method for moving a robot along a trajectory predetermined on a circularly moving workpiece, comprising the steps of: (a) teaching the robot of position of said predetermined trajectory in a stationary coordinate system when the workpiece remains stationary at a reference position;   (b) detecting an amount of revolution of the workpiece from said reference position while the workpiece is circularly moving;   (c) setting a rotary coordinate system which is obtained by revolving said stationary coordinate system by said amount of revolution detected in said step (b);   (d) successively calculating a robot position in said stationary coordinate system based on a robot position in said rotary coordinate system; and   (e) moving the robot along said predetermined trajectory based on the robot positions calculated in said step (d).   
     
     
       2. A robot tracking method for moving a robot along a trajectory predetermined on a circularly moving workpiece, comprising the steps of: (a) teaching the robot of position data of teaching points in said predetermined trajectory in a stationary coordinate system when the workpiece remains stationary at a reference position;   (b) detecting an amount of revolution of the workpiece from said reference position while the workpiece is circularly moving;   (c) obtaining position data of interpolation points based on said position data of said teaching points;   (d) successively executing revolution converting processing on said position data of interpolation points in accordance with said amount of revolution detected in said step (b), and successively determining the position of the robot based on the converted position data; and   (e) moving the robot along said predetermined trajectory based on the positions of the robot calculated in said step (d).